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Biomedical subjects

R J Linhardt

Publications and source records attributed to R J Linhardt.

At least 127 records · Page 7Linked to original sources
PubMed1993

Substrate specificity of the heparin lyases from Flavobacterium heparinum.

A detailed knowledge about the substrate specificities of the heparin lyases is necessary when using these enzymes as tools for elucidating the sequence of heparin and heparan sulfate. The substrate specificity of heparin lyases I, II, and III have been profiled with structurally defined, heparin-derived oligosaccharides. The primary substrate specificities of heparin lyases I and III require the presence of 2-O-sulfated alpha-L-idopyranosyluronic acid and beta-D-glucopyranosyluronic acid residues, respectively, at the linkages being cleaved. Heparin lyase II demonstrates an intriguingly broad primary specificity for oligosaccharides, acting at linkages containing alpha-L-idopyranosyluronic and beta-D-glucopyranosyluronic acid as well as at linkages containing alpha-L-galactopyranosyluronic acid residues. In addition to their primary specificities, each lyase also demonstrates secondary specificities under forcing conditions. Differences in the sulfation pattern within uronic acid residues and sulfation of adjacent residues has profound impact on the ease of lyase cleavage of a glycosidic linkage. Specifically, heparin lyases I and III exhibit secondary specificity for oligosaccharides containing an unsulfated alpha-L-idopyranosyluronic acid residue. The lack of sulfation on residues adjacent to the linkage undergoing cleavage increases the action of heparin lyase III on a glycosidic linkage. In contrast, reduced sulfation on adjacent residues make glycosidic linkage resistant to heparin lyase I. The primary and secondary specificity can be rationalized on the basis of most favorable solution conformation of the uronic acid residues.

Carbohydrate Conformation↗
PubMed1993

Specificity studies on the heparin lyases from Flavobacterium heparinum.

An understanding of the substrate specificity study of the heparin lyases (heparinase and heparitinases) is crucial for elucidation of the sequence of heparin and heparan sulfate. Four chemically modified heparins have been used to study the substrate specificity of the three heparin lyases. These modified heparins include the N- and O-desulfated and then specifically N-sulfated or N-acetylated derivatives of heparin and a modified heparin containing L-galactopyranosyluronic acid residues. These chemically modified heparins were degraded to various extents by the three heparin lyases. Differences in degree of sulfation have profound impact on the ease of cleavage of glycosidic linkages. Heparin lyase I (EC 4.2.2.7) is selective in cleaving highly sulfated polysaccharide chains containing linkages to 2-O-sulfated alpha-L-idopyranosyluronic acid residues. Heparin lyase III (EC 4.2.2.8) cleaves linkages that have reduced density of sulfation and that contain beta-D-glucopyranosyluronic acid residues. The ability of heparin lyase III to act on linkages to unsulfated alpha-L-idopyranosyluronic acid residues is observed for the first time. Heparin lyase II (no assigned EC number) demonstrates an unparalleled, wide specificity for substrates comprised of linkages containing both alpha-L-idopyranosyluronic and beta-D- glucopyranosyluronic acid residues. Heparin lyase II can also act on substrates containing linkages to unnatural alpha-L-galactopyranosyluronic acid residues. The high level of specificity of heparin lyase I makes it particularly suitable for use in the sequencing of heparin and heparan sulfate, while caution must be exercised in using heparin lyases II and III to sequence heparin and heparan sulfate because of their relatively broad specificity.

Acetylation↗
PubMed1993

Oligosaccharide composition of heparin and low-molecular-weight heparins by capillary electrophoresis.

The application of capillary electrophoresis to total compositional analysis of heparin and low-molecular-weight heparin samples has been studied. Optimum resolution of 17 defined oligosaccharides was obtained with the buffer system composed of 10 mM sodium borate and 50 mM sodium dodecyl sulfate at pH 8.81 and at a constant voltage of 20 kV. The ratio of oligosaccharide charge to the number of saccharide residues correlated with the migration time. For oligosaccharides having the same charge to saccharide ratio, the larger of the oligosaccharides eluted earlier. A hexasaccharide having a 3-O-sulfated glucosamine residue at the reducing end and arising from heparin's antithrombin III binding site, migrated in an unusual fashion. The limit of oligosaccharide detection was from 600 fmol to 1 pmol. Quantitative analysis could conveniently be performed on 10 pmol of an oligosaccharide sample. Oligosaccharide composition using capillary electrophoresis was obtained by nearly complete depolymerization of heparins with a mixture of heparin lyase I, II, and III. The analysis resulted in 95% mass balance for both heparin and low-molecular-weight heparin. Capillary electropherograms of heparin and different low-molecular-weight heparins depolymerized with heparin lyase I alone showed a high level of structural heterogeneity in the products formed. The oligosaccharide maps thus obtained might find use in fingerprinting the heparin and low-molecular-weight samples.

Carbohydrate Sequence↗
PubMed1993

Nature of the interaction of heparin with acidic fibroblast growth factor.

The binding of human acidic fibroblast growth factor (aFGF) to heparin has been analyzed by a variety of different approaches to better elucidate the nature of this protein/sulfated polysaccharide interaction. Static and dynamic light scattering as well as analytical ultracentrifugation analyses indicates that 14-15 molecules of a FGF can bind to a 16-kDa heparin chain, with approximately 10 of these bound relatively uniformly to high-affinity sites. The dissociation constants of these latter sites are estimated to be approximately 50-140 nM on the basis of surface plasmon resonance experiments in which the association and dissociation rates of aFGF interaction with immobilized heparin were measured. The size of the binding site of a FGF on heparin was also determined by heparin lyase digestion of a FGF/heparin complexes followed by isolation and characterization of protected oligosaccharides. The smallest aFGF-protected oligosaccharide comigrated with delta UA2S(1-->4)-alpha-D-GlcNp2S6S(1-->4)-alpha-L-IdoAp-2S( 1-->4)-alpha-D-GlcNp2S6S (where delta UA represents 4-deoxy-alpha-L-threo-hex-4-enopyranosyluronic acid and S is sulfate). Thus, aFGF appears to bind at high density (one molecule every 4-5 polysaccharide units) and with high affinity to heparin. This potentially provides a concentrated, stabilized storage form of the growth factor that can be released for receptor-mediated cellular activation in response to the proper stimuli. It is also possible that close proximity of aFGF molecules on the highly sulfated regions of heparan chains may be involved in the induction of receptor aggregation as suggested by Ornitz et al. [Ornitz, D. M., Yayon, A., Flanagan, J. G., Svahn, C. M., Levi, E., & Leder, P. (1992) Mol. Cell. Biol. 12, 240-247].

Binding Sites↗
PubMed1993

Degradation and release properties of pellets fabricated from three commercial poly(D,L-lactide-co-glycolide) biodegradable polymers.

Poly(D,L-lactide-co-glycolide, 50:50) samples of similar molecular weight were obtained from three commercial sources and were characterized by gel permeation chromatography, differential scanning calorimetry, X-ray powder diffraction, viscometry, and proton nuclear magnetic resonance spectroscopy. Pellets were prepared by melt-pressing spray-dried polymer with a 4-mm standard concave punch and die set and a thermostated holder of original design. Amaranth (5% w/w) was incorporated in pellets used for release studies. Degradation and release studies were conducted at 37 degrees C in pH 7.2 phosphate buffered saline. The molecular weights of all polymers were found to decrease continuously after exposure to phosphate buffered saline. All polymers showed two distinct regions of molecular weight decrease. Mass loss experiments for all polymers resulted in sigmoidal curves typical of polymers undergoing bulk hydrolysis. The onset of mass loss (defined as 10% mass loss) was found to differ by as much as 6 days among the three polymers studied. The release studies showed an initial burst of release followed by a period of 15-25 days during which little or no dye was released. A second phase of release followed, lasting approximately 10 days, until all dye was released. The time at which release began slightly preceded the onset of mass loss.

Buffers↗
PubMed1993

Physical stabilization of acidic fibroblast growth factor by polyanions.

Acidic fibroblast growth factor (aFGF) is markedly stabilized by heparin. Partially due to the heterogeneity of heparin preparations, the nature of the aFGF polyanion binding site is still ill-defined. We have, therefore, investigated a wide variety of well-defined polyanions in terms of their ability to stabilize human recombinant aFGF (15-154) against thermal denaturation. The specificity of the interaction between aFGF and polyanions is shown to be remarkably weak with a surprising number of polyanions (including small phosphorylated and sulfated compounds as well as highly charged biopolymers) able to induce physical stability. Temperature-dependent fluorescence and circular dichroism measurements show that many of these polyanionic compounds stabilize aFGF to the same extent as heparin. The ability of these agents to protect the three free thiol groups of aFGF from copper-catalyzed oxidation was also explored and significant protection was observed. The extent and electrostatic requirements of the protein's polyanion binding site were probed by the use of a series of well-defined heparin fragments and differentially phosphorylated inositol compounds. A tetrasaccharide fragment of heparin is the smallest unit of heparin capable of stabilizing aFGF against thermal denaturation. Increasing phosphorylation of inositol compounds (up to six phosphate groups per molecule) enhances the thermal stability of aFGF. These results are discussed in the context of a model of human aFGF based on the X-ray crystal structure of the bovine protein and previous studies by others of the heparin binding site of both acidic and basic FGF.

Amino Acid Sequence↗
PubMed1993

Monoclonal antibodies prepared against heparin lyase I and their reactivity toward heparin lyase I, II and III.

1. Six different monoclonal IgG mouse antibodies to heparin lyase I from Flavobacterium heparinum were prepared. 2. The monoclonal antibodies were used to detect heparin lyases I, II and III by dot-blotting immunoassay and by Western blotting. 3. Individual antibodies showed different reactivity toward the three heparin lyases. 4. The reactivity of two of the monoclonal antibodies was destroyed by exposing heparin lyases to sodium dodecyl sulfate. 5. The antibodies can be used to rapidly distinguish between the three heparin lyases.

Animals↗
PubMed1993

Capillary electrophoresis to measure sulfoesterase activity on chondroitin sulfate and heparin derived disaccharides.

Capillary electrophoresis was used to assay sulfoesterase activity on sulfated disaccharides derived from chondroitin sulfate, dermatan sulfate and heparin. The three sulfoesterases studied were chondro-4-O-sulfatase (EC 3.1.6.9) and chondro-6-O-sulfatase (EC 3.1.6.10) from Proteus vulgaris and heparo-2-O-sulfatase from Flavobacterium heparinum. Capillary electrophoresis was used to analyse sulfated disaccharide before and after sulfoesterase treatment and a change in migration time was indicative of the presence of sulfoesterase activity. This assay was used both on purified sulfoesterases and on minor sulfoesterase contaminants present in other enzyme preparations. The high sensitivity of capillary electrophoresis permits the elimination of 35S-radiolabeled substrates normally required to assay sulfoesterases. The high resolution of capillary electrophoresis allows the use of this assay on impure enzyme preparations containing high protein concentrations.

Chondro-4-Sulfatase↗
PubMed1992

Isolation and characterization of human heparin.

Heparin was isolated from an unusually large human hemangioma that contained an elevated level of mast cells. Purification of multimilligram quantities of heparin from this tissue sample permitted a thorough examination of its structure and activity. Characterization of this human heparin included the following: one-dimensional and two-dimensional 1H-nuclear magnetic resonance spectral analysis; oligosaccharide mapping; saccharide compositional analysis; and in vitro assessment and anticoagulant activity. Oligosaccharide mapping and nuclear magnetic resonance spectroscopy showed that this human heparin is structurally similar to porcine intestinal mucosal heparin but distinctly different from bovine lung heparin. This human heparin also has substantially more in vitro anticoagulant activity than either of these pharmaceutical heparins.

Animals↗
PubMed1992

Purification and characterization of heparin lyases from Flavobacterium heparinum.

Heparin lyase I has been purified from Flavobacterium heparinum and has been partially characterized (Yang, V. C., Linhardt, R. J., Berstein, H., Cooney, C. L., and Langer, R. (1985) J. Biol. Chem. 260, 1849-1857). There has been no report of the purification of the other polysaccharide lyases from this organism. Although all three of these heparin/heparan sulfate lyases are widely used, with the exception of heparin lyase I, there is no information on their purity or their physical and kinetic characteristics. The absence of pure heparin lyases and a lack of understanding of the optimal catalytic conditions and substrate specificity has stood in the way of the use of these enzymes as reagents for the specific depolymerization of heparin and heparan sulfate into oligosaccharides for structure and activity studies. This paper describes a single, reproducible scheme to simultaneously purify all three of the heparin lyases from F. heparinum to apparent homogeneity. Heparin lyase I (heparinase, EC 4.2.2.7), heparin lyase II (no EC number), and heparin lyase III (heparitinase, EC 4.2.2.8) have molecular weights (by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and isoelectric points (by isoelectric focusing) of M(r) 42,800, pI 9.1-9.2, M(r) 84,100, pI 8.9-9.1, M(r) 70,800, pI 9.9-10.1, respectively. Their amino acid analyses and peptide maps demonstrate that while these proteins are different gene products they are closely related. The kinetic properties of the heparin lyases have been determined as well as the conditions to optimize their activity and stability. These data should improve the application of these important enzymes in the study of heparin and heparan sulfate.

Amino Acid Sequence↗
PubMed1992

An electrophoresis-based assay for glycosyltransferase activity.

Polyacrylamide gel electrophoresis (PAGE) and capillary zone electrophoresis (CZE) were used to measure the activity of glycosyltransferases. Acceptor molecules were prepared by reductive amination of the monopotassium 7-amino-1,3-naphthalenedisulfonic acid (AGA) Schiff base with sugars. The resulting sugar conjugates were purified by gradient PAGE and recovered using semidry electrotransfer into a positively charged nylon membrane. The beta(1----4)galactosyltransferase was shown, by PAGE analysis, to transfer a beta-galactosyl residue to the AGA conjugate of beta-D-GlcNAc-(1----4)-beta-D-GlcNAc-(1----4)-D-GlcNAc (compound 4). Similarly, alpha(1----2)fucosyltransferase isolated from porcine submaxillary glands was shown to transfer fucose from GDP-fucose to the AGA conjugate of beta-D-Gal-(1----4)-beta-D-GlcNAc-(1----6)-D-Gal (compound 5). This conjugate (compound 5) was also an acceptor for the alpha(1----3/4)fucosyltransferase partially purified from human milk. The latter reaction was followed by both gradient PAGE and CZE, having sensitivities of 200 pmol and 80 fmol, respectively.

2-Naphthylamine↗
PubMed1992

Heparin and modified heparin inhibit complement activation in vivo.

Heparin regulates C activity in vitro, but has not been examined for this activity in vivo. The present study investigated the ability of commercial heparin and derivatized (N-desulfated, N-acetylated) heparin (Hep-NAc) with greatly diminished anticoagulant activity to inhibit C activation in guinea pigs. Catheters were placed in the right atrium of guinea pigs and kept patent with frequent saline flushes. The next day, heparin, Hep-NAc, or saline was given and 2.5 min later cobra venom factor or saline was given. Blood was drawn at intervals and assayed for total hemolytic C, C3 hemolytic activity, free hemoglobin, and activated partial thromboplastin time. Total hemolytic C and C3 activity decreased less rapidly in heparin- and Hep-NAc-pretreated animals than in non-pretreated animals, indicating that both heparins inhibited C activation. Heparin and Hep-NAc also inhibited cobra venom factor-induced hemolysis. This study demonstrates that commercial heparin and modified heparin inhibit C activation in vivo. This represents an important step in the development of an oligosaccharide drug to regulate C activation.

Animals↗
PubMed1992

Search for the heparin antithrombin III-binding site precursor.

The last step of heparin biosynthesis is thought to involve the action of 3-O-sulfotransferase resulting in the formation of an antithrombin III (ATIII) binding site required for heparin's anticoagulant activity. The isolation of a significant fraction of heparin chains without antithrombin III-binding sites and having low affinity for ATIII suggests the presence of a precursor site, lacking the 3-O-sulfate group. Porcine mucosal heparin was depolymerized into a mixture of oligosaccharides using heparin lyase. One of these oligosaccharides was derived from heparin's ATIII-binding site. In an effort to find the ATIII-binding site precursor, the structures of several minor oligosaccharides were determined. A greater than 90% recovery of oligosaccharides (on a mole and weight basis) was obtained for both unfractionated and affinity-fractionated heparins. An oligosaccharide arising from the ATIII-binding site precursor was found that comprised only 0.8 mol % of the oligosaccharide product mixture. This oligosaccharide was only slightly enriched in heparin having a low affinity for ATIII and only slightly disenriched in high affinity heparin. The small number of these ATIII-binding site precursors, found in unfractionated and fractionated heparins, suggests the existence of a low ATIII affinity heparin may not simply be the result of the incomplete action of 3-O-sulfotransferase in the final step in heparin biosynthesis. Rather these data suggest that some earlier step, involved in the formation of placement of these precursor sites, may be primarily responsible for high and low ATIII affinity heparins.

Animals↗
PubMed1992

Gradient polyacrylamide gel electrophoresis for determination of molecular weights of heparin preparations and low-molecular-weight heparin derivatives.

The M(r) values of pharmaceutical heparins and low-molecular-weight (LMW) heparin derivatives were examined as part of a collaborative study to develop methods for their characterization. Standard methods of M(r) determination rely on gel permeation high-performance liquid chromatography (HPLC). We report the use of gradient polyacrylamide gel electrophoresis (PAGE) to determine the M(r) values of pharmaceutical heparins and LMW heparin derivatives. This approach offers certain advantages over the HPLC method. Gradient PAGE analysis was performed in parallel, on multiple samples, with the same standard curve. HPLC was performed serially. Gradient PAGE gave higher resolution than HPLC, and thus, a mixture of easily obtained standards was used in place of individual standards for the construction of a standard curve. Heparin and various LMW heparin samples were analyzed by both gradient PAGE and conventional gel permeation HPLC methods. The number-average M(r), weight-average M(r), and polydispersity were examined by both techniques and found to be similar. This study demonstrates that gradient PAGE analysis is a sensitive method for the determination of the M(r) values of heparin and LMW heparin.

Carbohydrate Sequence↗